The following abbreviations and terms are herewith defined, at least some of which are referred to within the following description of the present disclosure.
3GPP 3rd-Generation Partnership Project
AB Access Bursts
AGCH Access Grant Channel
ASIC Application Specific Integrated Circuit
BLER Block Error Rate
BS Base Station
BSS Base Station Subsystem
CC Coverage Class
CDMA Code Division Multiple Access
CN Core Network
CRC Cyclic Redundancy Check
DL Downlink
DSP Digital Signal Processor
EDGE Enhanced Data rates for GSM Evolution
EGPRS Enhanced General Packet Radio Service
FDMA Frequency Division Multiple Access
FN Frame Number
GSM Global System for Mobile Communications
GERAN GSM/EDGE Radio Access Network
GPRS General Packet Radio Service
HARQ Hybrid Automatic Repeat Request
IoT Internet of Things
LTE Long-Term Evolution
MCS Modulation and Coding Scheme
MTC Machine Type Communications
PDN Packet Data Network
PTCCH Packet Timing Control Channel
RACH Random Access Channel
RAN Radio Access Network
TDMA Time Division Multiple Access
TSC Training Sequence Code
UE User Equipment
UL Uplink
WCDMA Wideband Code Division Multiple Access
WiMAX Worldwide Interoperability for Microwave Access
Coverage Class: At any point in time a device belongs to a specific uplink/downlink coverage class which determines the total number of blind transmissions to be used when transmitting/receiving radio blocks. An uplink/downlink coverage class applicable at any point in time can differ between different logical channels. Upon initiating a system access a device determines the uplink/downlink coverage class applicable to the RACH/AGCH based on estimating the number of blind repetitions of a radio block needed by the BSS receiver/device receiver to experience a BLER (block error rate) of approximately 10%. The BSS determines the uplink/downlink coverage class to be used by a device on the device's assigned packet channel resources based on estimating the number of blind repetitions of a radio block needed to satisfy a target BLER and considering the number of HARQ retransmissions (of a radio block) that will, on average, result from using that target BLER.
Extended Coverage: The general principle of extended coverage is that of using blind repetitions for the control channels and for the data channels. In addition, for the data channels the use of blind repetitions assuming MCS-1 (i.e., the lowest MCS supported in EGPRS today) is combined with HARQ retransmissions to realize the needed level of data transmission performance. Support for extended coverage is realized by defining different coverage classes. A different number of blind repetitions are associated with each of the coverage classes wherein extended coverage is associated with coverage classes for which multiple blind repetitions are needed (i.e., a single blind repetition is considered as the reference coverage). The number of total blind transmissions for a given coverage class can differ between different logical channels.
Internet of Things (IoT) devices: The Internet of Things (IoT) is the network of physical objects or “things” embedded with electronics, software, sensors, and connectivity to enable objects to exchange data with the manufacturer, operator and/or other connected devices based on the infrastructure of the International Telecommunication Union's Global Standards Initiative. The Internet of Things allows objects to be sensed and controlled remotely across existing network infrastructure creating opportunities for more direct integration between the physical world and computer-based systems, and resulting in improved efficiency, accuracy and economic benefit. Each thing is uniquely identifiable through its embedded computing system but is able to interoperate within the existing Internet infrastructure. Experts estimate that the IoT will consist of almost 50 billion objects by 2020.
Training Sequence Codes (TSCs): In GSM the training sequence is 26 bits long, and is included within bursts transmitted on a radio channel and is used by a receiver's equalizer as it estimates the transfer characteristic of the physical path between the BSS and a wireless device. The members of a set of TSCs are selected with the intent of each member having good autocorrelation and cross correlation properties which helps a receiver to better discriminate between the wireless devices on the same radio resource wherein different wireless devices can be assigned different TSC values.
A new cellular market segment known as Internet of Things (IoT) is exposing existing radio access technologies to new stringent requirements in terms of extended coverage and improved capacity.
To meet the first requirement of extended coverage, a typical approach used is to improve the robustness of existing radio channels through repetition based transmission schemes. To meet the second requirement of improved capacity, it is common to explore ways of increasing the multiplexing rate on channels through techniques such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA).
While requirements of high coverage and high capacity apply to most channels in cellular systems, one channel of particular interest is the Random Access Channel (RACH). The RACH is typically collision based, and used to support initial system access by wireless devices (e.g., IoT devices).
In light of the anticipated volume of IoT devices in the IoT market segment and their strict requirements, it is foreseeable that cellular radio access technologies will experience a dramatically increased load over the years to come. In addition to the large number of IoT devices requesting access to the cellular systems, it may be expected that the load will be further increased due to many wireless devices (including the IoT devices) operating in more challenging radio conditions wherein multiple repeated transmissions or a longer transmission time will be needed to achieve an acceptable performance (i.e., to realize sufficient coverage).
In the specific case of IoT, it may be anticipated that cellular systems need to support IoT devices of different coverage classes, as discussed in 3GPP TSG-GERAN Meeting #62 Work Item Description GP-140297, entitled “GSM optimization for Internet of Things” (the contents of which are hereby incorporated by reference) where from 1 to ‘N’ repeated transmissions will need to be sent by an IoT device for a single radio access event (e.g., a system access attempt on the RACH) depending on the coverage class of the IoT device. For example, while IoT devices in the best coverage class may only need a single transmission to convey a radio block, an IoT device in the worst coverage class may need to repeat the same radio block during 16 radio block transmission periods, for example, before the needed coverage can be achieved.
In the case of the collision based RACH, which is typically used for both autonomous device originated system access and system triggered (e.g., paging triggered) system access, it may be expected that the overall number of collisions will increase as a result of more IoT devices accessing the system using repetition based transmission schemes. More specifically, it is foreseeable that:                1. Collisions between system access attempts originating from IoT devices within the same coverage class will take place; and        2. Collisions between system access attempts originating from IoT devices from different coverage classes will take place.        
In the first case (i.e., collisions within the same coverage class), access bursts (ABs) sent over the RACH by two or more IoT devices may reach the receiving base station (BS) at similar power levels. Without a proper design of the access burst's training sequence codes (TSC), it will be difficult for the base station to correctly receive and equalize any of the colliding access bursts especially for the case where the colliding bursts make use of the same TSC. The IoT devices may then repeat their respective access attempts, thus further increasing the load on the RACH.
In the second case (i.e., collisions from different coverage classes), the power level from an access burst(s) of the IoT device from a better coverage class may be significantly stronger than the power level from the access burst(s) from the IoT device of a worse coverage class. In this case, the base station can with a high likelihood receive the stronger access burst(s) correctly, while the likelihood of a successful reception will be much lower for the weaker access burst(s) especially for the case where the colliding bursts make use of the same TSC.
In a population of IoT devices where most of the IoT devices will be of lower coverage classes (e.g., needing no repetitions or few repetitions), this may result in fewer but still a considerable amount of IoT devices with a higher coverage class (e.g., needed more repetitions) which will be experiencing a very limited system access success rate.
With all this in mind, it is foreseeable that a bottleneck may arise regarding the capacity of the RACH to support initial system accesses by IoT devices. Further, this is not a problem that is unique to IoT devices, and IoT traffic. A similar problem can be observed in any cellular system covering dense and crowded areas of wireless devices. This problem and other problems associated with the prior art are addressed in the present disclosure.